This invention relates in general to color systems for use in printing and, more particularly, to a system for softproofing a color reproduction.
In color printing processes (e.g., offset lithography, letterpress and gravure), it is customary to form three separate images by scanning the original through three different color filters to form three color separations. These three color separations are combined in various ways to produce printing plates or the equivalent thereof, which in turn control the amount of each colorant deposited at each point of the reproduction. A problem common to these processes is that the exact combination of colorants required for the match is not related to measurements which can be made on the original in any simple way. Great skill and experience are usually required on the part of the operator in adjusting the color printing system in order to achieve high quality reproduction of the original.
Even with highly qualified operators, the unpredictable behavior of color inks is such that proofing using actual inks is still a laborious and time-consuming process. For this reason, various softproofing systems have been developed to facilitate the proofing process. Softproofing systems typically include a color viewing device with which an image to be printed can be displayed by means of a color monitor. Extensive image corrections can then be made so that the corrected color image displayed on the color monitor comes as close as possible to the final printing result. In this manner, instead of having to go through the laborious and time-consuming process of proofing using actual inks, it is possible to predict the final printing result by observing the image as displayed on the color monitor. For an example of an apparatus for checking color pictures on a color monitor, please see U.S. Pat. No. 4,691,229 to Colditz et al.
In color monitors, color images are constructed from an array of square or rectangular pixels where each pixel includes fluorescent elements of different colors. In color reproduction systems, the colorants are typically printed in the form of circular dots. In order for the colorants in the form of circular dots to cover an entire area intended to be of a solid or mixed colors, the circular dots must overlap each other at least partially so as to leave no portion of the area not covered by the circular dots of colorants. For this reason, in almost all color reproducing systems, the dots overlap. Another major difference between color monitors and color reproducing systems is that in color monitors, the color of images displayed by color monitor are additive where the light of each color component is summed together whereas for printing systems, the ink mixtures are more nearly subtractive than additive, but the colors of overlapping areas are difficult to predict accurately because of non-ideal behavior of the inks. For this reason, where a circular dot of one colorant overlaps a circular dot of another colorant of a different color, the color of the overlapping area between the two dots may be difficult to predict accurately.
Conventional softproofing systems have not taken the above differences between color monitors and color reproducing systems using ink into account. For this reason, the color images displayed on the color monitor do not always accurately predict the appearance of the same image when printed using ink. It is therefore desirable to provide an improved softproofing system which enables the picture displayed on the color monitor to more accurately predict the final printing result.